We had some mould appear in our bathroom and I suspected that our inline extractor fan was underpowered. As it happens the extractor just stopped working, so I'm in the market for a replacement.

I have a few questions:

  • What is better - centrifugal or induct? It looks like the centrifugal ones have best throughput but are they as reliable etc?
  • What rate is good? I can't find info on my old induct 23W fan's rate, but I assume it was in the range 80-100 m^3/hr - does that sound about right? Would going up to a 220 m^3/hr be excessive?
  • Does power affect anything other than the rate?

A few notes:

  • The inlet in the bathroom is in the ceiling
  • I don't really want to take out the old ducting & fittings, so if it was a round, 125mm fan that would be great. Also 100mm would work I guess as I could still make the ducting fit.
  • Fan needs to have an adjustable timer on it so it stays on after the light is turned off - there is a permanent live circuit available.
  • Bathroom is approx 1.6m x 2.5m x 2.2m (i.e. 8.8 m^3) Using some recommendations from another answer, this would mean 70 m^3/hr would be fine... but it's not worked out that way before. Perhaps the timer wasn't on for long enough? Or perhaps I can double the throughput and halve the time?
  • 2
    How big is your bathroom?
    – Niall C.
    Sep 13, 2012 at 11:06
  • 2
    This answer might help you determine what size fan you need.
    – Tester101
    Sep 13, 2012 at 11:09
  • 2
    Whatever you do, pay close attention to the noise level. A fan that is too loud will not be used. Unfortunately, silence is golden. Which means it costs lots of gold. Sep 13, 2012 at 13:29
  • @NiallC - have added the info.
    – x3ja
    Sep 13, 2012 at 15:15
  • 3
    the other thing you need to take into account is how long the duct run is and how many bends are in it. Longer runs/more bends means you need a higher powered fan. Also make sure its not blocked!
    – Steven
    Sep 13, 2012 at 20:18

1 Answer 1


In the end I went for a mixed flow (which I think is both cetrifugal & radial or something), has about double the throughput that is recommended for the size of room (240 m^3/hr vs 110 m^3/hr). Doesn't have a timer on it, but it seems to be keeping the steam down when we shower anyway.

Here's a link to the fan I bought in the end.

Thanks for the pointers.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.